There are a number of documented attempts to build 7-segment displays in FischerTechnik. It turns out to be surprisingly difficult to do in a compact way. Driving seven different elements that are grouped in a not-so-easy pattern with a limited number of parts is hard. For the ones on the community, the driving part is multiple times larger than the display itself.
I tried myself, and it took many attempts. I must admit that the result isn't as reliabale as I would have liked it. Sometimes display elements fall over or are missed, but generally, it works and displays the time.